Assist feeding or force feeding is a last resort solution that is done when everything else has failed, which includes, downsizing enclosure to the smallest one available in this case 15 quarts tub, along with other things, like NO handling, feeding the proper prey (rats or mice) and the proper size and preferably live (medium mouse are too mall and will likely not be recognize as prey) etc

It is far from unusual for animals that age to go off feed with their new owner I have had several adults that came into my care that cease to eat anywhere for 6 months to a year before resuming feeding with me.

The key is PATIENCE